With the House controlled by Republicans, some environmentalists are urging President Obama to take action on climate change on his own. Here are five things he could do.

President Barack Obama has pledged to make addressing climate change a major priority in his second term. But House Republicans remain skeptical about both the problem and potential legislative solutions.

That's led many environmentalists to urge Obama to go it alone and take actions to reduce America's greenhouse gas emissions on his own. Below are five major things he could do without congressional approval.

Use the EPA's authority

In 2007, the Supreme Court ruled that the Environmental Protection Agency has the authority to regulate greenhouse gas emissions such as carbon dioxide under existing air pollution laws. The ruling empowered the agency to set higher standards for new power plants and write new regulations for older power plants.

Some environmentalists think Obama should take advantage of the EPA's newfound powers to restrict emissions as much as possible. That would still fall short of what a comprehensive bill passed through Congress could do, however, and it might spark a backlash from big business.

Reduce methane emissions

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Considered the second most significant greenhouse gas, methane is released from leaks in gas pipelines and coal mines, from landfills and livestock and agriculture. Some scientists think reducing methane in the atmosphere could delay the effects of climate change by as much as 15 years.

Obama could order the EPA, the Department of Energy and other federal agencies to refocus efforts at reducing methane emissions by capturing methane released at coal mines, reducing methane from landfills or even requiring more frequent draining of rice paddies.

Reduce soot

Soot, also known as black carbon, is another concern for environmentalists. One recent study argued that black carbon is a more dangerous greenhouse gas than methane because its color causes it to take in more solar radiation.

Obama could order federal agencies crack down on soot-emitting sources such as diesel engines, coal-fired power stations and coal-burning cookstoves. However, coal is already cleaner in the U.S. than it used to be, so there may be a limit on how much this can be addressed within the United States alone.

Approve more renewable energy

Obama can order government agencies to focus on climate change including the Department of Energy, that State Department and the Department of the Interior.

Between Interior and the Department of Agriculture, the government manages 700 million acres of land, with another 1.7 billion acres of offshore continental shelf managed by the Interior Department alone. Public lands are prime real estate when it comes to energy development, from coal mining to wind farms.

The administration could approve more renewable energy projects on federal lands. Though that would not subtract any greenhouse gas emissions from existing sources, it would reduce how many are added to the air in the future.

Reject the Keystone XL pipeline

Many environmentalists argue that the Obama administration needs to reject the proposed Keystone XL pipeline because it would promote the use of fossil fuels and create emissions from the extraction process. Still, there is uncertainty about how much the pipeline itself actually would increase oil sands production and how the oil it produces might end up being used.

Obama rejected the Keystone XL pipeline last year while in the midst of a re-election campaign, but the project is still alive. A number of senators have urged Obama to allow the pipeline, arguing they want to see energy resources developed in this country, but Obama will have a lot of power to block the pipeline if he wants.